The present invention relates to data storage devices such as a hard-disk drive (HDD), and more particularly to a data storage device that does not match in timing between data transfer from a controller such as a hard-disk controller (HDC), to a channel such as a read/write (R/W) channel, or vice versa, and the access (read/write) operation performed by the channel.
Devices using various types of media such as optical disks and magnetic tapes are known in the art as recording media drives provided in the interior or the exterior of information processing apparatuses. Among them, hard disk drives (hereinafter referred to as HDDs) have become popular as storage devices for information processing apparatuses to such an extent that they are one type of the storage devices indispensable for today's information processing systems. Further, not limited to the information processing apparatuses as described above, HDDs are expanding more and more in application. For example, HDDs are used for moving picture recording/reproducing devices, car navigation systems, cellular phones, and removable memories for use in them.
These HDDs record on magnetic disks the user data transferred from PCs or other hosts, read out the user data recorded on the magnetic disks, and transfer the data to the hosts. The magnetic disks used in an HDD each have a plurality of concentrically formed tracks. The regions in which servo data that is the address information required for the positioning of a magnetic head is recorded (i.e., servo regions) are arranged intermittently across tracks, and the regions between servo regions function as data regions in which user data and the like will be recorded. Also, one data region sandwiched between servo regions includes a plurality of sectors, and the head can access desired data sectors by using servo data to perform user data read/write operations on the sectors. When data is recorded, one data sector may be split into two sections across a servo region. Such sectors are called split sectors.
Read/write operation of the HDD with respect to a magnetic disk thereof is controlled by a data storage control circuit (more specifically, an HDC and an R/W channel). When a write operation is performed on the magnetic disk, the hard-disk controller (HDC) of the HDD receives user data from a host and then adds an error correction code (ECC) to the received user data. The user data to which ECC has been added is transferred from the HDD through a data bus of about 10 bits, called the NRZ (Non-Return to Zero) bus, to the read/write (R/W) channel. Hereinafter, the user data transferred in an ECC-added condition from the HDD to the R/W channel is called NRZ data. The R/W channel performs an encoding process to convert the NRZ data that has been received from the HDC, into a data format (channel codes) suitable for recording on the magnetic disk. Encoded data is written onto the magnetic disk by the head.
For conventional HDDs, since a writing delay time associated with an encoding process or the like by an R/W channel and a readout delay time associated with a decoding process are not too long, an HDC allows for a delay time subsequent to R/W channel processing and outputs a Write Gate (WG) signal and a Read Gate (RG) signal. Thus, the timing of data transfer between the HDC and the R/W channel and the timing of physical writing onto/readout from a magnetic disk are controlled (refer to, for example, Patent Document 1 (Japanese Patent Laid-open No. 2001-167524) and Patent Document 2 (Japanese Patent Laid-open No. 2004-234779)).
For writing onto the magnetic disk, a write instruction based on the WG signal is given and at the same time, the NRZ data to be written is transferred from the HDC to the R/W channel. Next, the R/W channel provides the NRZ data with an encoding process and a data conversion process such as conversion into serial data, whereby the NRZ data is actually written onto the magnetic disk. For data readout from the magnetic disk, the R/W channel initiates the data readout, pursuant to a readout command based on the RG signal, and then conducts required signal processing such as waveform shaping and decoding. The NRZ data that has thus been restored to its original format is transferred from the R/W channel to a host.
Decoding in the R/W channel, however, tends to be complicated for improved restoration accuracy of the data read out by the R/W channel, and this is creating a tendency for a decoding delay time to further increase. Along with this, the code block length, which is the data unit of encoding, also increases. In addition, an encoding delay time in the R/W channel tends to increase as a result.
If the encoding delay time and decoding delay time in the R/W channel actually increase in this way, in write mode, for example, there will be an even greater difference in time from the start of NRZ data transfer to the R/W channel by the HDC after it has issued a write instruction based on the WG signal, to physical writing onto the magnetic disk. In readout mode, there will also be an even greater difference in time from the start of physical reading from the magnetic disk after a readout instruction based on the RG signal has been issued, to the start of NRZ data transfer from the R/W channel.
If the encoding delay time and decoding delay time in the R/W channel increase as mentioned above, the write operation and the readout operation cannot be sufficiently controlled in the conventional control method that uses the WG and RG signals to define both the write/readout instruction to the R/W channel and the start of NRZ data transfer.
Accordingly, studies are being performed on a method of controlling independently the timing of NRZ data transfer between the HDC and the R/W channel, and the timing of the read/write operation by the R/W channel. More specifically, this method uses a signal that defines the data transfer timing independently of the WG and RG signals. In write mode, for example, data transfer from the HDC to the R/W channel is started prior to the issuance of a write instruction based on the WG signal.